Process for preparing pyridine bases

ABSTRACT

A process for preparing simultaneously pyridine bases including 2-methylpyridine and 4-methylpyridine, occasionally, together with pyridine from acetaldehyde and ammonia by gas phase catalytic reaction, characterized in that the gas phase catalytic reaction is conducted in the presence of a catalyst prepared by (A) incorporating at least one compound containing at least one metal selected from the group consisting of tungsten, manganese, nickel, iron, cobalt, molybdenum, uranium, lead, silver, copper and tin into silica-alumina simultaneously with preparation of the silica-alumina, or (B) subjecting silica-alumina to ion exchange with ions of at least one metal selected from the group consisting of manganese, nickel, iron, cobalt, uranium, lead, silver, copper and tin to adsorb the ions on said silica-alumina. According to the process of the present invention, there can be obtained the desired pyridine bases in high yield, whereas formation of by-products including high boiling point pyridine derivatives is remarkably suppressed. The catalyst employed in the present process has a high resistance to the reaction atmosphere.

This is a division of application Ser. No. 841,083, filed Oct. 11, 1977now U.S. Pat. No. 4,179,576 issued Dec. 18, 1979.

The present invention relates to a process for preparing pyridine basesfrom acetaldehyde and ammonia by gas phase catalytic reaction. Moreparticularly, the invention relates to a process for preparingsimultaneously 2-methylpyridine and 4-methylpyridine, or simultaneously2-methylpyridine, 4-methylpyridine and pyridine.

Pyridine bases are valuable intermediates for use in production of dyes,medicines, agricultural chemicals and the like, and they are importantalso as solvents. Moreover, corresponding vinyl monomers are preparedfrom 2- or 4-methylpyridines, and their application fields are nowexpanding because such vinyl monomers are suitable as comonomers forproduction of synthetic rubbers or synthetic fibers.

The process for preparing pyridine bases from acetaldehyde and ammoniaby gas phase catalytic reaction is known as Chichibabin process, and itsvarious improved processes have been proposed. In these known processes,however, the yields of pyridine bases, especially 2-methylpyridine,4-methylpyridine and pyridine are relatively poor, and by-products whichrender the purification step difficult, such as high boiling pointpyridine bases, e.g., 2-methyl-5-ethylpyridine,4-methyl-3-ethylpyridine, 4-propylpyridine and 2-propylpyridine, andother tar-like by-products are formed in large quantities. Moreover,catalysts used in these known processes have poor resistance to fouling.

It is therefore a primary object of the present invention to provide aprocess for preparing pyridine bases, especially 2-methylpyridine,4-methylpyridine and pyridine, in high yields from acetaldehyde andammonia by gas phase catalytic reaction using a durable catalyst to thisreaction.

Another object of the present invention is to provide a process in whichformation of high boiling point pyridine bases can be suppressed in theabove gas phase catalytic reaction.

In general, the mechanism for formation of pyridine bases fromacetaldehyde and ammonia is considered to include a complex combinationof aldol condensation, Michael condensation and similar reactions. It isconsidered that when these condensation reactions are effected by thegas phase catalytic reaction, acid sites of the solid catalyst act asactive points. Accordingly, the activity or performance of the catalystused varies greatly depending on the number and intensity of acid sitesof the solid catalyst.

The inventors of the present invention made investigations, usingsilica-alumina as the solid acid, on modification of this solid acid,especially on methods for modifying the solid acidity of silica-alumina.As a result, they found an optimum combination of a specific modifyingmetal with a specific modifying method, and succeeded in developing aprocess in which the yeilds of pyridine bases (exclusive of high boilingpoint pyridine bases) can be increased to those as high as 87%. Based onthese findings, they have now completed the present invention.

More specifically, in accordance with the present invention, there isprovided a process for preparing pyridine bases from acetaldehyde andammonia by gas phase catalytic reaction, wherein the gas phase catalyticreaction is carried out at a temperature of 300° to 550° C. and at aspace velocity of 200 to 10,000 hr⁻¹ in the presence of a catalystprepared by (A) incorporating at least one compound containing at leastone metal selected from the group consisting of tungsten, manganese,nickel, iron, cobalt, molybdenum, uranium, lead, silver, copper and tininto silica-alumina simultaneously with preparation of thesilica-alumina, or (B) subjecting silica-alumina to ion exchange withions of at least one metal selected from the group consisting ofmanganese, nickel, iron, cobalt, uranium, lead, silver, copper and tinto adsorb the ions on said silica-alumina.

As mentioned above, in the present invention there is employed acatalyst comprising silica-alumina and at least one modifying metalselected from the group consisting of W, Mn, Ni, Fe, Co, Mo, U, Pb, Ag,Cu and Sn in the form of a compound or ion.

In the catalyst of the present invention, it is preferred that thesilica/alumina weight ratio is in the range of from 98/2 to 50/50,especially from 95/5 to 70/30.

When the modifying metal is incorporated in the form of a compound, itis advantageous that the metal compound should be incorporated in anamount of 1 to 70 parts by weight per 100 parts by weight of the sum ofsilica and alumina. When the modifying metal is selected from W, Mn, Co,Pb, U, Cu and Ag and it is incorporated in the form of a compound, it ispreferred that the amount of the metal compound is 1 to 50 parts byweight per 100 parts by weight of the sum of silica and alumina. When ametal selected from the group consisting of Ni, Fe, Mo and Sn is used asthe modifying metal and it is incorporated in the form of a compound, itis preferred that the compound is incorporated in an amount of 1 to 20parts by weight per 100 parts by weight of the sum of silica andalumina. As the modifying metal to be incorporated in the form of acompound, there are advantageously employed W, Pb and Sn.

When the modifying metal is incorporated in the form of an ion by ionexchange adsorption, the adsorbed amount of the metal is generally 0.01to 1.2 milliequivalents per gram of silica-alumina. When a metalselected from Pb, Mn, Co, U and Ag is used as the modifying metal, it ispreferred that the adsorbed amount of the metal is 0.1 to 1.2milliequivalent per gram of silica-alumina, and when a metal selectedfrom Ni, Fe and Sn is used as the modifying metal, it is preferred thatthe adsorbed amount of the metal is 0.1 to 0.5 milliequivalent per gramof silica-alumina. As the modifying metal to be incorporated in the formof an ion, there are advantageously employed Pb and Sn.

As mentioned hereinbefore, the catalyst used in the present invention isprepared according to any of the following two methods:

(A) The modifying metal is incorporated in the form of a compound intosilica-alumina simultaneously with preparation of the silica-alumina.

(B) The modifying metal is incorporated in the form of an ion insilica-alumina by ion exchange adsorption.

These two methods will now be described in detail.

Method (A)

A compound of a modifying metal present in a catalyst prepared accordingto the method (A) should be stable at the reaction temperature.Accordingly, oxides, sulfates, phosphates, halides and metal oxyacidsalts of modifying metals are preferable. Some of such sulfates,phosphates, halides and metal oxyacid salts are water soluble, and someof them are relatively water-insoluble. Specifically stated, it ispreferred that the modifying metals are present in the catalyst in theform of oxides such as WO₃, MnO, NiO, Fe₂ O₃, CoO, MoO₃, U₃ O₈, PbO, Ag₂O, CuO and SnO, sulfates such as MnSO₄, NiSO₄, Fe₂ (SO₄)₃, CoSO₄, UO₂SO₄, PbSO₄, Ag₂ SO₄ and CuSO₄, phosphates such as Mn₃ (PO₄)₂, Ni₃(PO₄)₂, FePO₄, Co₃ (PO₄)₂, Pb₃ (PO₄)₂ and Ag₃ PO₄, halides such asMnCl₂, MnF₂, NiCl₂, NiF₂, NiBr₂, FeF₃, CoCl₂, CoF₂, CoBr₂, UO₂ Cl₂,PbCl₂, PbF₂, AgCl, AgF, AgBr, SnF₂, CuCl, CuF and CuBr, and metaloxyacid salts such as Na₂ WO₄, CaWO₄, FeWO₄, NiWO₄, PbWO₄, CoWO₄, Na₂MoO₄, PbMoO₄, NiMoO₄ and CaMoO₄.

It is believed that in catalysts prepared according to the method (A),the modifying metals are present in the form of any of the foregoingcompounds. It is also believed that more stable compounds may be formedby the reaction with silica, alumina, silicate ion, aluminum ion and thelike, or by the change of the valency of the metal by calcination.

According to the method (A), as mentioned hereinbefore, it is essentialthat a compound of a modifying metal is incorporated into silica-aluminasimultaneously with preparation of the silica-alumina. Statedillustratively, the three kinds of materials, namely silica source,alumina source and compound of modifying metal are put together and thecompound of modifying metal is incorporated into the silica and thealumina. That is, simultaneously with the time when silica-alumina isprepared, for example, by a mixing method, a precipitation method, acogelation method or the like, a compound of a modifying metal to bepresent in the resulting catalyst as it is or a precursor of saidcompound (a compound to be converted to the intended compound at thestep of gel formation or calcination, for example, ammonium tungstate tobe converted to the intended compound, tungsten oxide) is incorporatedinto silica and alumina and made copresent therewith. Differentlystated, there are employed a method in which the compound of themodifying metal is incorporated, as it is, into the silica-alumina atthe preparation of the latter to obtain a catalyst having the metalcompound in the form of a water-soluble or relatively water-insolublecompound; and a method in which the precursor of the intended compoundcontaining the modifying metal is incorporated in the silica-alumina atthe preparation of the latter to obtain a catalyst having the metalcompound in the form of an oxide. In this case, the precursor isconverted to said intended compound, for example the oxide at the stageof calcination.

As the silica source, there may be used silica hydrogel, silica sol,sodium silicate, alkylsiloxanes, silicon tetrachloride, etc., and as thealumina source, there may be used alumina hydrogel, alumina sol,aluminum salts such as aluminum sulfate, aluminum chloride and aluminumnitrate, sodium aluminate, aluminum isopropoxide, etc.

In preparing the catalyst according to the method (A), the modifyingmetal may be used in the form of a water-soluble compound and added to areaction mixture for forming silica-alumina. Organic and inorganic saltsmay be used as the water-soluble compound. As the organic salt,water-soluble formic acid salts, acetic acid salts, propionic acidsalts, lactic acid salts, oxalic acid salts and citric acid salts arepreferably used. As the inorganic salt, water-soluble nitrates,sulfates, halides and metal oxyacid salts are preferably used. Morespecifically, there are preferably employed manganese formate, nickelformate, ferric formate, cobalt formate, uranyl formate, cupric formate,manganese acetate, nickel acetate, ferric acetate, cobalt acetate,uranyl acetate, cupric acetate, lead acetate, stannous acetate, silveracetate, manganese propionate, cobalt propionate, manganese lactate,ferric lactate, silver lactate, ferric oxalate, ferric citrate, cobaltcitrate, Mn(NO₃)₂, Ni(NO₃)₂, Fe(NO₃)₃, Co(NO₃)₂, Cu(NO₃)₂, Pb(NO₃)₂, UO₂(NO₃)₂, AgNO₃, MnSO₄, NiSO₄, Fe₂ (SO₄)₃, CoSO₄, UO₂ SO₄, CuSO₄, MnCl₂,NiCl₂, FeCl₃, CoCl₂, UO₂ Cl₂, CuCl₂, SnCl₂, ammonium paratungstate,ammonium paramolybdate, sodium tungstate, potassium tungstate, sodiummolybdate and potassium molybdate, alone or in mixture.

When the modifying metal is to be in the form of an oxide in theresulting catalyst, the metal compound may be once converted to ahydroxide by neutralization or the like, unless it provides an oxide bycalcination in the air. In general, the starting metal compounds arepreferably to be converted to a hydroxide by neutralization or the like.The conversion to hydroxide may be effected by adjusting the pH ofaqueous solution of the metal compounds more than 6, or more preferablyto 6 to 8. Moreover, the water-soluble compounds as given above may beemployed in the form of a hydroxide slurry formed by hydrolysis of thecompounds.

When a water-soluble compound of the modifying metal, other than anoxide, namely, a sulfate, phosphate, halide and metal oxyacid salt, ispresent in the resulting catalyst, a compound stable at the reactiontemperature is chosen from the water-soluble compounds as given above,and silica-alumina is prepared in the presence of this compound. As thespecific example of the compound stable at the reaction temperature,MnSO₄, NiSO₄, Fe₂ (SO₄)₃, CoSO₄, UO₂ SO₄, CuSO₄, MnCl₂, NiCl₂, CoCl₂,CoBr₂, UO₂ Cl₂, NaWO₄ and the like, are preferred. They may be employedalone or in mixture.

When a relatively water-insoluble compound of the modifying metal, otherthan an oxide, namely, a sulfate, phosphate, halide and metal oxyacidsalt, is included in the resulting catalyst, silica-alumina is preparedin the presence of a water-soluble compound as given above while addinga precipitating agent to convert the water-soluble compound to theintended relatively water-insoluble compound. When a chlorideprecipitate such as PbCl₂ or AgCl, for example, is to be included in thecatalyst, HCl, NaCl, KCl and the like are used as the precipitatingagents; when a fluoride precipitate such as MnF₂, NiF₂, FeF₃, CoF₂,PbF₂, AgF or SnF₂ is incorporated in the resulting catalyst, NaF, NH₄ F,KF and the like are used as the precipitating agents. When a sulfateprecipitate such as PbSO₄ or Ag₂ SO₄ is incorporated in the resultingcatalyst, H₂ SO₄, Na₂ SO₄ and the like are used as the precipitatingagents; when a phosphate precipitate such as Mn₃ (PO₄)₂, Ni₃ (PO₄)₂,FePO₄, Co.sub. 3 (PO₄)₂ or Pb₃ (PO₄)₂ is included in the resultingcatalyst, H₃ PO₄, Na₃ PO₄, K₃ PO₄, (NH₄)₃ PO₄, Na₂ HPO₄, K₂ HPO₄, (NH₄)₂PO₄ and the like are used as the precipitating agents.

Methods similar to the mixing, precipitation and cogelation methodsadopted for preparation of silica-alumina are used for the production ofthe catalyst of the present invention. The following methods are theexamples to be employed to prepare a catalyst in this invention. (1)When the modifying metal is present in the form of an oxide in the finalcatalyst:

(a) An aqueous solution of a compound of the modifying metal is added toa mixture of silica in the form of silica hydrogel and/or silica sol andalumina in the form of alumina hydrogel and/or alumina sol. Theresulting mixture is sufficiently stirred by means of a stirrer, kneaderor the like, and the pH is adjusted to at least 6, preferably 6 to 8.The stirring is further conducted; the resulting gelatinous slurry isfiltered; the recovered solid is sufficiently washed with water anddried at 80° to 130° C. for 4 to 10 hours. Then, the particle size isadjusted by pulverization or the dried solid is shaped according to acustomary method. Finally, the pulverized or shaped solid is calcined at350° to 550° C. for 4 to 8 hours.

(b) An aqueous solution of an aluminum salt and an aqueous solution of acompound of the modifying metal are simultaneously added to silicahydrogel and/or silica sol, and the resulting liquid is sufficientlymixed. Then, the pH is adjusted to at least 6, preferably 6 to 8, andthe mixing is further conducted sufficiently. The resulting gelatinousslurry is then treated in substantially the same manner as described in(a) above.

(c) An aqueous solution of sodium silicate, an aqueous solution of analuminum salt and an aqueous solution of a compound of the modifyingmetal are mixed together in a container in which mixing is done in ashort time, for example, with a mixer, and the pH is adjusted to atleast 6, preferably 6 to 8. Then, the mixing is further conductedsufficiently. The resulting gelatinous slurry is then treated insubstantially the same manner as described in (a) above.

(d) In any of the foregoing methods (a) to (c), a slurry of a hydroxideof the modifying metal, which has been prepared by hydrolysis inadvance, is used in place of the aqueous solution of the modifying metalcompound. The slurry is then treated in substantially the same manner asdescribed in any of (a) to (c) above.

In each of the foregoing methods, the pH adjustment is accomplished byusing an acid or alkali. As the acid, an aqueous solution ofhydrochloric acid, sulfuric acid, nitric acid, acetic acid or the likeis preferably used. As the alkali, an aqueous solution of sodiumhydroxide, potassium hydroxide, ammonia or the like is preferably used.Some modifying metals form relatively insoluble salts or soluble complexsalts with a certain acid or alkali. Therefore, a suitable acid or saltshould be used to prevent formation of such metal compounds other thanmetal hydroxy precipitates. (2) When the modifying metal is present inthe form of a water-soluble compound other than an oxide in the finalcatalyst:

An aqueous solution of a compound of the modifying metal is added to amixture of silica in the form of silica hydrogel and/or silica sol andalumina in the form of alumina hydrogel and/or alumina sol, and themixture is sufficiently stirred by means of a stirrer, kneader or thelike. Even if silica sol or alumina sol is used as the silica or aluminasource, the metal compound to be added simultaneously acts as anelectrolyte and breaks down the ionic balance which has stabilizedcolloidal particles. Thus, gelation of silica and alumina sols maysufficiently advances. Even if gelation does not take place, it isadvantageous to cause gelation by heating under such conditions as willnot modify the metal compound by hydrolysis or double decomposition, orto cause gelation by adding a metal-free coagulant. The resultinggelatinous slurry is subjected to filtration and the recovered solid isappropriately washed with water under such conditions as will not causecomplete dissolution of the metal compound contained therein. The washedsolid is then treated in substantially the same manner as described in(1)-(a) above.

Metal compounds such as MnSO₄, NiSO₄, Fe₂ (SO₄)₃, CoSO₄, UO₂ SO₄, CuSO₄,MnCl₂, NiCl₂, CoCl₂, NiBr₂, CoBr₂, UO₂ Cl₂, Na₂ WO₄, and Na₂ MoO₄, forexample, are suitable to be incorporated in the resulting catalystaccording to the method (2). (3) When the modifying metal is present inthe form of a relatively water-insoluble compound in the final catalyst:

An aqueous solution of a precursor of the intended compound of themodifying metal compound is added to a mixture of silica in the form ofsilica hydrogel and/or silica sol and alumina in the form of aluminahydrogel and/or alumina sol, and the mixture is sufficiently stirred bya stirrer, kneader or the like. Then a pecipitating agent capable ofdouble-decomposing with the precursor of the intended compound of themodifying metal and precipitating the modifying metal in the form of arelatively water-insoluble salt is added to the mixture. The resultinggelatinous slurry is sufficiently stirred and filtered, and therecovered solid is sufficiently washed with water and then treated insubstantially the same manner as described in (1)-(a) above.

As the compound of the modifying metal that is included in the resultingcatalyst according to this method, there can be mentioned, for example,PbSO₄, Ag₂ SO₄, MnF₂, NiF₂, FeF₃, CoF₂, PbF₂, AgF, CuF, SnF₂, PbCl₂,AgCl, CuCl, AgBr, CuBr, Mn₃ (PO₄)₂, Ni₃ (PO₄)₂, FePO₄, Co₃ (PO₄)₂, Pb₃(PO₄)₂, Ag₃ PO₄, CaWO₄, PbWO₄, FeWO₄, MnWO₄, CoWO₄, PbMoO₄, NiMoO₄ andCaMoO₄.

As will be apparent from the foregoing illustration, according to themethod (A), the modifying metal is incorporated in the form of acompound in the catalyst simultaneously with preparation ofsilica-alumina.

Method (B)

According to the method (B), the modifying metal is incorporated in theform of an ion in the catalyst of the present invention by ion exchangeadsorption. By the term "ion exchange adsorption" is meant the operationor reaction for making ions of the modifying metal adsorbed tightly onsilica-alumina at its acid sites while forming a metal salt ofsilica-alumina according to ion exchange, and by the term "ionexchange-adsorbed state" is meant the state where ions of the modifyingmetal are strongly adsorbed on silica-alumina at its acid sites in theform of a metal salt of silica-alumina. In the catalyst prepared by themethod (B), it is exactly unknown but believed that the modifying metalis ion exchange-adsorbed on silica-alumina substantially in the form ofan ion, but a part of the modifying metal may be contained in themetallic state or in the form of a compound.

In the catalyst prepared according to the method (B), the modifyingmetal is ion exchange-adsorbed on silica-alumina in the form of an ion.However, if a solution containing the modifying metal ion that is to beincorporated in a silica-alumina catalyst according to the presentinvention is directly treated with silica-alumina, the modifying metalion is hardly ion exchange-adsorbed on the silica-alumina. Accordingly,there is adopted a method in which a solution containing an ion capableof being directly ion exchange-adsorbed on silica-alumina is firsttreated with silica-alumina to convert the ion to a salt ofsilica-alumina and then a solution containing the modifying metal ion istreated with silica-alumina and adsorbed thereon by ion exchangeadsorption. As the ion capable of being directly ion exchange-adsorbedon silica-alumina (hereinafter referred to as "medium ion"), there canbe mentioned, for example, Li⁺, Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺ and NH₄ ⁺. Amongthese medium ions, an ammonium ion is most preferred.

According to the method (B), by dipping silica-alumina in an aqueoussolution containing 0.1 to 2.0 moles/liter of a medium ion or passingthis aqueous solution through a column packed with silica-alumina,silica-alumina is converted to a silica-alumina salt of the medium ion.In this case, it is preferred that calcined silica-alumina is used asthe silica-alumina. When the so formed silica-alumina salt of the mediumion (medium ion type silica-alumina) is contacted with an aqueoussolution containing a modifying metal ion, cation exchange reaction iscaused between the medium ion and the modifying metal ion to providesilica-alumina having the modifying metal ion exchange-adsorbed thereon.

Cation exchange can be performed by a customary batch method or a columnmethod. According to the batch method, medium ion type silica-alumina isdipped in an aqueous solution containing modifying metal ions. Accordingto the column method, medium ion type silica-alumina is packed in acolumn and development is carried out with an aqueous solutioncontaining modifying metal ions.

As the aqueous solution containing modifying metal ions, there can beused aqueous solutions of organic and inorganic salts of the modifyingmetal. As the organic salt, there are preferably employed a formic acidsalt, an acetic acid salt, a propionic acid salt, a lactic acid salt, anoxalic acid salt and a citric acid salt. As the inorganic salt, thereare preferably employed a nitric acid salt, a sulfuric acid salt, ahalide and an ammonium complex salt. More specifically, aqueoussolutions of manganese formate, nickel formate, ferric formate, cobaltformate, uranyl formate, cupric formate, manganese acetate, nickelacetate, iron acetate, cobalt acetate, copper acetate, lead acetate,manganese propionate, manganese lactate, iron lactate, iron oxalate,iron citrate, Mn(NO₃)₂, Ni(NO₃)₂, Fe(NO₃)₃, Co(NO₃)₂, Cu(NO₃)₂,Pb(NO₃)₂, UO₂ (NO₃)₂, AgNO₃, MnSO₄, NiSO₄, Fe₂ (SO₄)₃, CoSO₄, UO₂ SO₄,CuSO₄, MnCl₂, NiCl₂, FeCl₃, CoCl₂, UO₂ Cl₂, CuCl₂, CuCl, SnCl₂,[Co(NH₃)₆ ]Cl₂, [Ni(NH₃)₆ ]Cl₂, [Ag(NH₃)₂ ]Cl and [Cu(NH₃)₂ ]Cl arepreferably employed.

In general, the concentration of the aqueous solution is adjusted to0.01 to 2.0 moles/liter as the salt, and it is preferred that theconcentration of the aqueous solution is in the range of from 0.05 to0.5 mole/liter. It also is preferred that the amount of the modifyingmetal ions in the aqueous solution is in the range of from 1 to 50millimoles per gram of silica-alumina. The pH of the modifying metalion-containing aqueous solution is adjusted to a range in whichhydrolysis of the metal ions is not caused. The pH adjustment isaccomplished by an acid or alkali. As the acid, there are employedaqueous solutions of hydrochloric acid, sulfuric acid, nitric acid,acetic acid and the like, and as the alkali, there are used aqueoussolutions of ammonia, sodium hydroxide, potassium hydroxide and thelike. However, use of a combination of a modifying metal and an acid oralkali, which will result in formation of a relatively water-insolublesalt, should be avoided.

When two or more modifying metal ions are ion exchange-adsorbed insilica-alumina, the foregoing procedures are conducted by using anaqueous solution of mixed salts. However, in the cases where arelatively water-insoluble salt is formed or unavoidable hydrolysistakes place, there may be adopted a staged method in which one modifyingmetal ion is adsorbed by ion exchange and after sufficientwater-washing, the other modifying metal ion is adsorbed by ionexchange.

It is preferred that the so formed modifying metal ion typesilica-alumina is sufficiently washed with deionized water until a metalion is not detected in the washing water. The so formed modifiedsilica-alumina is then dried at 80° to 130° C. for 2 to 10 hours, andafter it has been molded into tablets according to need, it is calcinedat 300° to 550° C. for 4 to 8 hours.

The catalyst according to the above-mentioned method (B) isdistinguishable over a catalyst prepared according to a customaryimpregnation method. More specifically, even if silica-alumina is dippedin an aqueous solution of the above-mentioned metal salt that is used inthe present invention according to the customary impregnation technique,the above-mentioned ion exchange adsorption is not caused but the metalsalt is merely deposited on the surface of silica-alumina. Accordingly,in this state, bonding between the modifying metal and silica-alumina isvery weak and the modifying metal is readily dissolved out by waterwashing. In contrast, in the present invention, since silica-alumina isfirst converted to a medium ion type silica-alumina by treatingsilica-alumina with an aqueous solution containing medium ions and thismedium ion type silica-alumina is reacted with an aqueous solutioncontaining modifying metal ions to form silica-alumina having themodifying metal ions adsorbed thereon by ion exchange, bonding betweenthe modifying metal ions and silica-alumina is very strong and themodifying metal ions are not dissolved out by water-washing.

In the instant specification, the so prepared catalyst is expressed asSA-M(n) in which M represents a modifying metal ion and n indicates thevalency of the modifying metal ion, and the catalyst prepared byimpregnation is expressed as SA-MX in which MX represents a metalcompound.

In practising the process of the present invention, the catalystprepared according to the method (A) or (B) is packed in a reaction tubeand the starting material vapor is fed to the reaction tube whilemaintaining the catalyst layer at 300° to 550° C. It is preferred thatthe starting material vapor is preheated to 300° to 550° C. prior tointroduction to or contact with the catalyst layer. Deposition of acrystal of acetaldehyde ammonium which may cause clogging in pipes canbe avoided by preheating acetaldehyde and ammonia independently to atemperature of at least 200° C. and then mixing them. A high temperaturevapor coming from the reaction tube is condensed by a cooler. Results ofthe reaction can be grasped by gas chromatograph analysis of theproduct.

As the starting material, there may be used acetaldehyde per se or acompound capable of being decomposed at the reaction temperature toprovide acetaldehyde. Namely, paraaldehyde or metaaldehyde may be used.

The molar ratio of ammonia to acetaldehyde is generally at least 0.3,preferably in the range of 0.5 to 3.0.

The reaction may be carried out in the presence or absence of an inertsubstance which is gaseous at the reaction temperature and does notparticipate directly in the reaction. Since the present reaction ishighly exothermic, it is preferred to remove the heat generated by thereaction. Therefore, the reaction is preferably carried out in thepresence of an inert gas such as steam, nitrogen, argon or helium as adiluent. In general, the inert gas is present in an amount of 0 to 90%by volume based on the starting material vapor. It is preferred that theamount of the inert gas is 25 to 85% by volume based on the startingmaterial vapor.

The reaction may be carried out under reduced or elevated pressure,namely under a pressure of 0.1 to 10 atmospheres, but in general, thereaction is conducted under atmospheric pressure.

As mentioned hereinbefore, the reaction temperature at which the processof the present invention is worked is in the range of 300° to 550° C.,and it is preferred that the reaction is carried out at 350° to 550° C.When the reaction temperature is too low, the conversion is low andacetaldehyde is mainly recovered in the form of acetaldehyde ammonium,and when the reaction temperature is too high, decomposition orcarbonization of the product is remarkably increased and the yield ofthe intended product is lowered.

It is important that the process of the present invention is conductedat a space velocity of 200 to 10,000 hr⁻¹, preferably 400 to 2,000 hr⁻¹.An optimum space velocity is varied depending on the reactiontemperature, the kind and particle size of the catalyst used, the gascomposition and other factors but the optimum velocity can readily bedetermined by conducting simple experiments while fixing the foregoingconditions. In general, if the space velocity is lower than 200 hr⁻¹,even after complete conversion the product gas is kept in contact withthe catalyst, resulting in advance of decomposition and carbonization ofthe resulting pyridine base. At a space velocity higher than 10,000hr⁻¹, the conversion is low. In each case, the yield of the intendedproduct is lowered. The space velocity referred to the instantspecification and claims is expressed in a value defined by thefollowing formula:

Space Velocity=A/B

wherein A stands for the total volume of the starting material fed tothe reactor for every one hour, as calculated as in the normal state andB designates the apparent volume of the catalyst in the reactor.

The yields of pyridine, 2-methylpyridine and 4-methylpyridine and ofhigh boiling point pyridine bases are expressed in terms of molar yieldscalculated based on the assumption that pyridine, 2-methylpyridine and4-methylpyridine are formed in a total amount of 1 mole from 3 moles ofacetaldehyde and that 1 mole of methylethylpyridine representing highboiling point pyridine bases is formed from 4 moles of acetaldehyde.

The performance of the catalyst prepared according to the method of thepresent invention is much higher than that of a catalyst preparedaccording to the customary impregnation method, when they contain thesame modifying metal, which will readily be understood from the testresults shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                          Yields (%) of Products                                                              2-methyl-                                                                              4-methyl-                                    Catalyst Preparation Method                                                                           pyridine pyridine                                                                             total                                 ______________________________________                                        SiO.sub.2                                                                              method(A) of   33.7     46.1   79.8                                  Al.sub.2 O.sub.3WO.sub.3                                                               present invention                                                    SAWO.sub.3                                                                             impregnation   20.5     20.7   41.2                                           method                                                                ##STR1##                                                                                method (B) of                                                                               43.1     39.5   82.6                                          present invention                                                    SAPbO    impregnation   29.4     25.4   54.8                                           method                                                                        Reaction temperature:                                                                        440° C.                                                 Space velocity:                                                                              800hr.sup. -1                                         ______________________________________                                         (Data shown in Table 1 are maximum yields obtained in experiments             conducted by the inventors of the present invention.)                    

In the catalyst prepared according to the impregnation method, themodifying metal compound only adheres to silica-alumina, and it is notdistributed uniformly but unevenly in an islands-in-sea manner.Therefore, the effect of the modifying metal compound cannot bemanifested sufficiently.

On the other hand, in the catalyst prepared according to the method (A)of the present invention, silica, alumina and the modifying metalcompound are mixed together highly homogeneously. Also in such catalyst,it is construed that active sites are acid sites generated by bonding ofsilica and alumina. However, when bonding of silica and alumina isformed, since the modifying metal is included in the skeleton structureof silica-alumina, acid sites generated by bonding of silica and aluminaare influenced in a complicated manner by the included modifying metalcompound and the resulting catalyst shows a solid acidity different fromthat of the conventional silica-alumina catalyst.

In the catalyst prepared according to the method (B) of the presentinvention, the modifying metal ions are adsorbed on silica-alumina byion exchange. Shirasaki et al. Catalyst, 9, 85 (1967) teach that in suchcatalyst, the metal ions are uniformly dispersed and distributed and thesolid acidity of silica-alumina is influenced in a complicated manner byion exchange adsorption of the metal ions. Accordingly, the catalystprepared according to the method (B) of the present invention hascatalytic properties quite different from those of the silica-aluminasubstrate.

The above-mentioned differences between the catalyst prepared accordingto the present invention and the catalyst prepared according to thecustomary impregnation method become conspicuous when the content of themodifying metal is increased. In the catalyst prepared according to theimpregnation method, the modifying metal compound merely adheres to thesurface of silica-alumina, and the content of the modifying metalcompound should naturally be limited. More specifically, if themodifying metal compound is included in a large quantity, the modifyingmetal compound coats the surface of silica-alumina, and the activity ofthe resulting catalyst is degraded. In contrast, according to the methodof the present invention, it is possible to increase the amount of themodifying metal compound or ion without degradation of the activity ofthe catalyst, and the modifying effect is further enhanced.

In the catalyst prepared according to the present invention, the effectof the modifying metal can be enhanced with increase of the content ofthe modifying metal. When Fe, Ni, Mo or Sn is used as the modifyingmetal, if the content of the modifying metal is too high, acetonitrileis readily formed as a by-product and the yield of the intended pyridinebases is lowered. Accordingly, when a modifying metal as mentioned aboveis employed, an optimum content of the modifying metal is relativelylow.

Among catalysts that are used in the process of the present invention,those containing at least one modifying metal selected from Ag and Cucan enhance the yield of pyridine among the yields of the intendedpyridine bases. In this case, it is preferred to adopt the method (B)for the preparation of the catalyst, and it also is preferred that thevalency of Ag and Cu is 1. Moreover, when Ag or Cu is used as the firstmetal, it is preferred that at least one second metal selected from thegroup consisting of Sn, Pb, Mn, Cd, Zn, Co, Ni, Fe, alkali metals suchas Na and K and alkaline earth metals such as Ca and Mg is used incombination with the first metal. In this case, the total yield ofpyridine, 2-methylpyridine and 4-methylpyridine can be further improved.In catalysts of this type, it is preferred that the content of the firstmetal is 0.1 to 1.0 milliequivalent per gram of silica-alumina, thecontent of the second metal is 0.01 to 1.0 milliequivalent per gram ofsilica-alumina and the total content of the first and second metals isup to 1.2 milliequivalent per gram of silica-alumina. Among the secondmetals as given above, Pb, Sn, Ca and Cd may be most advantageouslyemployed.

In the process of the present invention, the yield of the intendedpyridine bases can be remarkably improved as mentioned hereinbefore, andin addition, the resistance of the catalyst can also be improvedremarkably. More specifically, when the reaction is conducted for 10hours by using a customary silica-alumina catalyst, the total yield of2-methylpyridine and 4-methylpyridine is reduced to 30.1% from theinitial value of 43.9%; namely, the yield is reduced by 31% based on theinitial value. In contrast, in a SiO₂ -Al₂ O₃ -WO₃ catalyst preparedaccording to the method (A) of the present invention, the yield isreduced only to 73.6% from the initial value of 79.1%, and reduction ofthe yield is only 7% based on the initial value. Further, in a SA-Pb(II) catalyst prepared according to the method (B), the yield is reducedto 79.6% from the initial value of 83.0% and reduction of the yield isonly 4% based on the initial value. This prominent improvement of theyield is deemed to be due to the fact that the selectivity to theintended reaction is enhanced to reduce formation of high boiling pointpyridine bases and carbonization is hardly caused on the surface of thecatalyst. In the present invention, the degraded catalyst can easily beregenerated by passing streams of an oxygen-containing gas through thedegraded catalyst.

The present invention will now be described in detail by reference tothe following Examples that by no means limit the scope of theinvention.

Unless otherwise specified, the percentage, part, ratio etc. appearingin the Examples are given by weight.

EXAMPLE 1

A solution of 97.9 parts of aluminum sulfate [Al₂ (SO₄)₃. 16-18H₂ O] in500 ml of water and a solution of 30 parts of ammonium paratungstate in2,000 ml of warm water were added to 283 parts of silica sol having asilica content of 30%, and the resulting mixture was agitated for 2hours. Then, the pH of the mixture was adjusted to 8 by addition ofaqueous ammonia, whereby the liquid mixture was gelled. The gelledslurry was agitated for 4 hours and allowed to stand still at roomtemperature for two days and two nights.

The resulting gel was subjected to filtration, and the recovered solidwas sufficiently washed, dried at 100° C. for 4 hours, pulverized andcalcined for 4 to 8 hours in an air current. The so obtained catalysthad a silica/alumina/tungsten oxide ratio of 85/15/25.

A reaction tube was packed with 100 ml of the so prepared catalyst, anda gas phase catalytic reaction was carried out while introducing a gasmixture of acetaldehyde and ammonia (1:1.5) at a reaction temperature of430° C. and a space velocity of 1,000 hr⁻¹. As a result,2-methylpyridine and 4-methylpyridine were obtained in yields of 33.2%and 35.8%, respectively, and the total yield of the two pyridine baseswas 69.0%.

EXAMPLE 2

By using the same catalyst as used in Example 1, a gas phase catalyticreaction was carried out while introducing a gas mixture ofacetaldehyde, ammonia, steam and nitrogen (1:1:4:2 by volume) at areaction temperature of 440° C. and a space velocity of 800 hr⁻¹. Theyields of 2-methylpyridine and 4-methylpyridine were 33.7% and 46.1%,respectively, and the total yield of the two pyridine bases was 79.8%.

EXAMPLE 3

By using a catalyst prepared substantially the same method as describedin Example 1, which has a silica/alumina/tungsten oxide ratio of85/15/4, a gas phase catalytic reaction was carried out under the samereaction conditions as described in Example 2. As a result,2-methylpyridine and 4-methylpyridine were obtained in yields of 24.3%and 32.5%, respectively, and the total yield of the two pyridine baseswas 56.8%.

COMPARATIVE EXAMPLE 1

A gas phase catalytic reaction was carried out under the same conditionsas described in Example 2 by using silica-alumina andsilica-alumina-tungsten oxide catalysts prepared according to theimpregnation method. Obtained results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                         Yields (%) of Products                                                              2-methyl-                                                                              4-methyl-                                     Run No.                                                                              Composition of Catalyst                                                                       pyridine pyridine                                                                             total                                  ______________________________________                                        1      SA-WO.sub.3 (100:4)                                                                           20.5     20.7   41.2                                   2      SA-WO.sub.3 (100:10)                                                                          16.4     16.4   32.8                                   3      SA (85:15)      16.2     24.7   40.9                                   ______________________________________                                         SA has a silica/alumina ratio of 85/15                                   

EXAMPLE 4

By using a catalyst having a silica/alumina/tungsten oxide ratio of75/25/25, which was prepared in substantially the same manner asdescribed in Example 1, a gas phase catalytic reaction was carried outunder the same conditions as described in Example 2. As a result,2-methylpyridine and 4-methylpyridine were obtained in yields of 30.4%and 31.5%, respectively, and the total yield of the two pyridine baseswas 61.9%.

EXAMPLE 5

By using catalysts containing a metal oxide indicated in Table 3, whichwere prepared in substantially the same manner as described in Example1, gas phase catalytic reactions were carried out under the sameconditions as described in Example 2 to obtain results shown in Table 3.The precursors of the metal oxides and their amounts added are asfollows:

Run No. 1: 40 parts of manganese nitrate

Run No. 2: 20 parts of nickel nitrate

Run No. 3: 25 parts of ferric nitrate

Run No. 4: 35 parts of uranyl nitrate

Run No. 5: 20 parts of stannous chloride

Run No. 6: 40 parts of lead nitrate

                  TABLE 3                                                         ______________________________________                                                         Yields (%) of Products                                                              2-methyl-                                                                              4-methyl-                                     Run No.                                                                              Composition of Catalyst                                                                       pyridine pyridine                                                                             total                                  ______________________________________                                        1      SiO.sub.2 --Al.sub.2 O.sub.3 --MnO                                                            27.6     35.9   63.5                                   2      SiO.sub.2 --Al.sub.2 O.sub.3 --NiO                                                            28.1     34.5   62.6                                   3      SiO.sub.2 --Al.sub.2 O.sub.3 --Fe.sub.2 O.sub.3                                               27.0     32.9   59.9                                   4      SiO.sub.2 --Al.sub.2 O.sub.3 --U.sub.3 O.sub.8                                                26.0     34.8   60.8                                   5      SiO.sub.2 --Al.sub.2 O.sub.3 --SnO                                                            30.0     35.4   65.4                                   6      SiO.sub.2 --Al.sub.2 O.sub.3 --PbO                                                            33.1     35.2   68.3                                   ______________________________________                                    

EXAMPLE 6

Catalysts containing molybdenum oxide in an amount of 5, 10, 20, 40parts per 100 parts of the sum of silica and alumina were prepared insubstantially the same manner as described in Example 1 by usingammonium paramolybdate as the precursor of molybdenum oxide. By usingthree catalysts, gas phase catalytic reactions were carried out underthe same conditions as described in Example 2 to obtain results shown inTable 4.

                  TABLE 4                                                         ______________________________________                                        Composition     Yields (%) of Products                                        Run  of Catalyst    2-methyl-                                                                              4-methyl    aceto-                               No.  SiO.sub.2                                                                            Al.sub.2 O.sub.3                                                                      MoO.sub.3                                                                           pyridine                                                                             pyridine                                                                             total                                                                              nitrile                          ______________________________________                                        1    85     15       5    28.2   32.0   60.2 3.8                              2    85     15      10    30.3   33.2   63.5 6.2                              3    85     15      20    28.0   27.6   55.6 15.4                             4    85     15      40    20.4   19.8   40.2 27.2                             ______________________________________                                    

EXAMPLE 7

A slurry was prepared by mixing 283 parts of silica sol having a silicacontent of 30% with 150 parts of alumina sol having an alumina contentof 10% sufficiently, and an aqueous solution of 30 parts of manganesechloride in 500 ml of water was promptly added to the slurry. Gelationtook place, but the gelled slurry was agitated sufficiently to obtain ahomogeneous gelatinous slurry. The slurry was allowed to stand still for2 days and nights, and the gel was recovered by filtration, washed with1,000 ml of deionized water three times, dried at 100° C. for 4 hours,pulverized and calcined at 500° C. for 4 hours. In the resultingcatalyst, the silica/alumina/manganese chloride ratio was 85/15/23.

By using the so obtained catalyst, a gas phase catalytic reaction wascarried out under the same conditions as described in Example 2. As aresult, 2-methylpyridine and 4-methylpyridine were obtained in yields of26.0% and 39.3%, respectively, and the total yield of the two pyridinebases was 65.3%.

EXAMPLE 8

A catalyst was prepared in substantially the same manner as described inExample 7 except that 30 parts of manganese sulfate was used instead ofthe manganese chloride used in Example 7, and by using the so preparedcatalyst, a gas phase catalytic reaction was carried out under the sameconditions as described in Example 2. As a result, 2-methylpyridine and4-methylpyridine were obtained in yields of 24.6% and 32.0%,respectively, and the total yield of the two pyridine bases was 56.6%.

EXAMPLE 9

A slurry was prepared by mixing 283 parts of silica sol having a silicacontent of 30% sufficiently with 150 parts of alumina sol having analumina content of 10%, and an aqueous solution of 30 parts of manganesesulfate in 500 ml of water was promptly added to the slurry to obtain agelatinous slurry, and while the resulting slurry was sufficientlyagitated, an aqueous solution of 10 parts of ammonium fluoride in 100 mlof water was added thereto. The agitation was further conducted for 4hours and the mixture was allowed to stand still for two days and twonights. The gel was recovered by filtration, washed sufficiently withdeionized water, dried at 100° C. for 4 hours, pulverized and calcinedat 500° C. for 4 hours to obtain a catalyst having asilica/alumina/manganese fluoride ratio of 85/15/10.

By using the so prepared catalyst, a gas phase catalytic reaction wascarried out under the same conditions as described in Example 2 toobtain 2-methylpyridine and 4-methylpyridine in yields of 36.2% and34.0%, respectively. The total yield of the two pyridine bases was70.2%.

EXAMPLE 10

A catalyst having a silica/alumina/lead fluoride ratio of 85/15/18 wasprepared in substantially the same manner as described in Example 9except that 30 parts of lead nitrate was used instead of the manganesesulfate. By using the so prepared catalyst, a gas phase catalyticreaction was carried out under the same conditions as described inExample 2 to obtain 2-methylpyridine and 4-methylpyridine in yields of37.0% and 34.3%, respectively. The total yield of the two pyridine baseswas 71.3%.

EXAMPLE 11

A catalyst having a silica/alumina/lead phosphate ratio of 85/15/20 wasprepared in substantially the same manner as described in Example 9except that 30 parts of lead nitrate was used instead of the manganesesulfate and 40 parts of 30% phosphoric acid was used instead of theammonium fluoride. By using the so prepared catalyst, a gas phasecatalytic reaction was carried out under the same conditions asdescribed in Example 2 to obtain 2-methylpyridine and 4-methylpyridinein yields of 35.4% and 32.8%, respectively. The total yield of the twopyridine bases was 68.2%.

EXAMPLE 12

Pelletized silica-alumina (having an alumina content of 13%) having asize of 1 mm, which had been calcined at 500° C. for 4 hours in anelectric furnace, was dipped in 1 N aqueous ammonia for 7 days and thenair-dried to obtain ammonium type silica-alumina.

A glass column having an inner diameter of 30 mm was packed with 100 mlof the so prepared ammonium type silica-alumina and 2,000 ml of anaqueous solution containing 0.4 mole of lead nitrate was developed overa period of 7 days. The so treated silica-alumina was washedsufficiently with deionized water until the lead ion was not detected inthe washing liquid. Then, the treated silica-alumina was dried at 90° to100° C. for 4 hours and calcined at 500° C. for 4 hours to obtain acatalyst containing 1.0 milliequivalent of lead per gram ofsilica-alumina.

A gas phase catalytic reaction was carried out under the same conditionsas described in Example 2 by using the so prepared catalyst to obtain2-methylpyridine and 4-methylpyridine in yields of 43.1% and 39.5%,respectively. The total yield of the two pyridine bases was 82.6%. Theyields of pyridine and high boiling point pyridine bases were 0.8% and1.2%, respectively.

EXAMPLE 13

Catalysts containing 0.4 milliequivalent and 0.2 milliequivalent of leadper gram of silica-alumina, respectively, were prepared in substantiallythe same manner as described in Example 12, and by using the so preparedcatalysts, gas phase catalytic reactions were carried out under the sameconditions as described in Example 2 to obtain results shown in Table 5.

COMPARATIVE EXAMPLE 2

By using catalysts containing 0.2 and 0.4 millimole of lead oxide pergram of silica-alumina, which were prepared according to theimpregnation method and the silica-alumina, respectively, gas phasecatalytic reactions were carried out under the same conditions asdescribed in Example 2 to obtain results shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________                    Yields (%) of Products                                                                  high boiling                                                                        2-methylpyridine                                              2-methyl-                                                                          4-methyl-                                                                          point pyri-                                                                         plus 4-methyl-                                Catalyst        pyridine                                                                           pyridine                                                                           dine  pyridine                                      __________________________________________________________________________     Run No. 1 of                                                                         ##STR2##                                                                               39.2                                                                               37.1                                                                               1.8   76.3                                         Example 13                                                                           (Pb content                                                                   of 0.4 meq/g                                                                  of SA)                                                                  Run No. 2 of                                                                         ##STR3##                                                                               35.6                                                                               34.9                                                                               2.5   70.5                                         Example 13                                                                           (Pb content                                                                   of 0.2 meq/g                                                                  of SA)                                                                 Run No. 1 of                                                                         SAPbO (PbO                                                                             26.3 19.9 6.5   46.2                                          Comparative                                                                          content of                                                             Example 2                                                                            0.4 milli-                                                                    mole/g of                                                                     SA)                                                                    Run No. 2 of                                                                         SAPbO (PbO                                                                             29.4 25.4 9.8   54.8                                          Comparative                                                                          content of                                                             Example 2                                                                            0.2 milli-                                                                    mole/g of                                                                     SA)                                                                    Run No. 3 of                                                                         SA       16.9 24.0 10.2  40.9                                          Comparative                                                                   Example 2                                                                     __________________________________________________________________________

EXAMPLE 14

Catalysts having a modifying metal ion adsorbed thereon by ion exchangewere prepared in substantially the same manner as described in Example12, and by using the so prepared catalysts, gas phase catalyticreactions were carried out under the same conditions as described inExample 2 to obtain results shown in Table 6. The catalysts used for thereaction are as follows:

Run No. 1:

A catalyst having a manganese content of 0.65 milliequivalent per gramof silica-alumina was prepared in substantially the same manner asdescribed in Example 12 except that 2,000 ml of an aqueous solutioncontaining 0.3 mole of manganese nitrate was used instead of the aqueoussolution of lead nitrate.

Run No. 2:

A catalyst having a cobalt content of 0.6 milliequivalent per gram ofsilica-alumina was prepared in substantially the same manner asdescribed in Example 12 except that 2,000 ml of an aqueous solutioncontaining 0.3 mole of cobalt nitrate was used instead of the aqueoussolution of lead nitrate.

Run No. 3:

A catalyst having a nickel content of 0.25 milliequivalent per gram ofsilica-alumina was prepared in substantially the same manner asdescribed in Example 12 except that 2,000 ml of an aqueous solutioncontaining 0.1 mole of nickel nitrate was used instead of the aqueoussolution of lead nitrate.

Run No. 4:

A catalyst having an iron content of 0.28 milliequivalent per gram ofsilica-alumina was prepared in substantially the same manner asdescribed in Example 12 except that 2,000 ml of an aqueous solutioncontaining 0.1 mole of iron nitrate was used instead of the aqueoussolution of lead nitrate.

Run No. 5:

A catalyst having a lead content of 0.5 milliequivalent per gram ofsilica-alumina and a nickel content of 0.2 milliequivalent per gram ofsilica-alumina was prepared in substantially the same manner asdescribed in Example 12 except that 2,000 ml of an aqueous solutioncontaining 0.2 mole of lead nitrate and 0.1 mole of nickel nitrate wasused instead of the aqueous solution of lead nitrate.

Run No. 6:

A catalyst having a silver content of 1.1 milliequivalent per gram ofsilica-alumina was prepared in substantially the same manner asdescribed in Example 12 except that 2,000 ml of an aqueous solutioncontaining 0.8 mole of silver nitrate was used instead of the aqueoussolution of lead nitrate.

Run No. 7:

A catalyst having a copper content of 0.7 milliequivalent per gram ofsilica-alumina was prepared in substantially the same manner asdescribed in Example 12 except that 2,000 ml of 4 N ammonia solutioncontaining 0.8 mole of cuprous chloride and 1.0 mole ammonium chloridewas used instead of the aqueous solution of lead nitrate.

Run No. 8:

A catalyst having a copper content of 0.85 milliequivalent per gram ofsilica-alumina was prepared in substantially the same manner asdescribed in Example 12 except that 2,000 ml of an aqueous solutioncontaining 0.4 mole of cupric nitrate was used instead of the aqueoussolution of lead nitrate.

                                      TABLE 6                                     __________________________________________________________________________                   Yields (%) of Products                                                                             pyridine +                                                                    2-methyl-                                                               high boiling                                                                        pyridine +                                                    2-methyl-                                                                          4-methyl-                                                                          point pyri-                                                                         4-methyl-                                 Run No.                                                                            Catalyst  Pyridine                                                                           pyridine                                                                           pyridine                                                                           dine bases                                                                          pyridine                                  __________________________________________________________________________     1                                                                                  ##STR4##  5.0  29.5                                                                               40.1                                                                               4.6   74.6                                      2                                                                                  ##STR5##  3.0  27.8                                                                               36.2                                                                               4.3   67.0                                      3                                                                                  ##STR6##  3.0  29.7                                                                               32.1                                                                               3.0   64.8                                      4                                                                                  ##STR7##  3.5  28.7                                                                               32.7                                                                               2.7   64.9                                      5                                                                                  ##STR8##  1.2  40.8                                                                               38.6                                                                               2.8   80.6                                      6                                                                                  ##STR9##  13.8                                                                               23.6                                                                               34.4                                                                               2.5   71.8                                      7                                                                                  ##STR10##                                                                               10.5                                                                               21.7                                                                               30.2                                                                               2.8   62.4                                      8                                                                                  ##STR11##                                                                               7.4  22.8                                                                               32.4                                                                               5.6   62.6                                     __________________________________________________________________________

EXAMPLE 15

Catalysts containing tin in an amount of 0.06, 0.25, 0.43 and 0.6milliequivalent per gram of silica-alumina, respectively, were preparedin substantially the same manner as described in Example 12 except thatan aqueous solution of stannous chloride-hydrochloric acid was usedinstead of the aqueous solution of lead nitrate. Gas phase catalyticreactions were carried out under the same conditions as described inExample 2 by using the so prepared catalysts to obtain results shown inTable 7.

                                      TABLE 7                                     __________________________________________________________________________    Sn Content   Yields (%) of Products                                                (meq/g. SA)          high boiling                                              ##STR12##                                                                             2-methyl-                                                                          4-methyl-                                                                             point pyri-                                                                         aceto-                                       Run No.                                                                            Catalyst                                                                              pyridine                                                                           pyridine                                                                           total                                                                            dine bases                                                                          nitrile                                       __________________________________________________________________________    1    0.06    31.1 32.4 63.5                                                                             3.4    1.3                                          2    0.25    42.0 38.6 80.6                                                                             2.5    4.2                                          3    0.43    34.6 29.4 64.0                                                                             2.0   12.8                                          4    0.6     25.9 20.4 46.3                                                                             1.8   23.5                                          __________________________________________________________________________

EXAMPLE 16

Catalysts having a silver ion and other metal ion indicated in Table 8,which were absorbed by ion exchange, were prepared in substantially thesame manner as described in Example 12, and by using the so preparedcatalysts gas phase catalytic reactions were carried out under the sameconditions as described in Example 2 to obtain results shown in Table 8.The used catalysts are as follows:

Run No. 1:

A catalyst containing 0.6 milliequivalent of silver and 0.45milliequivalent of lead per gram of silica-alumina was prepared insubstantially the same manner as described in Example 12 except that2,000 ml of an aqueous solution containing 0.4 mole of silver nitrateand 0.2 mole of lead nitrate was used instead of the aqueous solution oflead nitrate.

Run No. 2:

A catalyst containing 0.6 milliequivalent of silver and 0.25milliequivalent of cadmium per gram of silica-alumina was prepared insubstantially the same manner as described in Example 12 except that2,000 ml of an aqueous solution containing 0.4 mole of silver nitrateand 0.2 mole of cadmium nitrate was used instead of the aqueous solutionof lead nitrate.

Run No. 3:

A catalyst containing 0.6 milliequivalent of silver and 0.5milliequivalent of calcium per gram of silica-alumina was prepared insubstantially the same manner as described in Example 12 except that anaqueous solution containing 0.4 mole of silver nitrate and 0.2 mole ofcalcium nitrate was used instead of the aqueous solution of leadnitrate.

Run No. 4:

A catalyst containing 0.5 milliequivalent of silver and 0.5milliequivalent of strontium per gram of silica-alumina was prepared insubstantially the same manner as described in Example 12 except that 0.4mole of silver nitrate and 0.2 mole of strontium nitrate were usedinstead of the aqueous solution of leas nitrate.

Run No. 5:

A catalyst containing 0.6 milliequivalent of silver and 0.45milliequivalent of manganese per gram of silica-alumina was prepared insubstantially the same manner as described in Example 12 except that anaqueous solution containing 0.4 mole of silver nitrate and 0.2 mole ofmanganese nitrate was used instead of the aqueous solution of leadnitrate.

Run No. 6:

A catalyst containing 0.6 milliequivalent of silver and 0.35milliequivalent of zinc per gram of silica-alumina was prepared insubstantially the same manner as described in Example 12 except that anaqueous solution containing 0.4 mole of silver nitrate and 0.2 mole ofzinc nitrate was used instead of the aqueous solution of lead nitrate.

                                      TABLE 8                                     __________________________________________________________________________                 Yields (%) of Products                                                                             pyridine +                                                              high boiling                                                                        2-methylpyri-                               Run               2-methyl-                                                                          4-methyl-                                                                          point pyri-                                                                         dine + 4-me-                                No.                                                                              Catalyst  pyridine                                                                           pyridine                                                                           pyridine                                                                           dine bases                                                                          thylpyridine                                __________________________________________________________________________     1                                                                                ##STR13##                                                                               12.5                                                                               38.1                                                                               37.0                                                                               2.0   87.6                                        2                                                                                ##STR14##                                                                               11.9                                                                               35.3                                                                               36.7                                                                               2.2   83.9                                        3                                                                                ##STR15##                                                                               12.4                                                                               34.8                                                                               40.0                                                                               3.0   87.2                                        4                                                                                ##STR16##                                                                               12.7                                                                               26.8                                                                               37.6                                                                               2.8   77.1                                        5                                                                                ##STR17##                                                                               13.6                                                                               26.2                                                                               35.7                                                                               2.3   75.5                                        6                                                                                ##STR18##                                                                               10.2                                                                               27.8                                                                               35.0                                                                               2.9   73.0                                       __________________________________________________________________________

EXAMPLE 17

A glass column was packed with 100 ml of ammonium type silica-aluminaprepared in substantially the same manner as described in Example 12,and 2,000 ml of an aqueous solution containing 0.4 mole of silvernitrate was developed over a period of 7 days. The so treatedsilica-alumina was washed with deionized water until the silver ion wasnot detected in the washing liquid. Then, 2,000 ml of 1 N aqueoushydrochloric acid containing 0.2 mole of stannous chloride was developedover a period of 7 days, and the treated silica-alumina was sufficientlywashed with deionized water until no stannous ion was detected in thewashing liquid. The so treated silica-alumina was dried and calcined inthe same manner as described in Example 12 to obtain a catalystcontaining 0.5 milliequivalent of silver and 0.3 milliequivalent of tinper gram of silica-alumina.

By using the so prepared catalyst, a gas phase catalytic reaction wascarried out under the same conditions as described in Example 12 toobtain pyridine, 2-methylpyridine and 4-methylpyridine in yields of10.4%, 33.6% and 34.8%, respectively. The total yield of these productswas 78.8% but the yield of high boiling point pyridine bases was only1.2%.

EXAMPLE 18

Pelletized silica-alumina (having an alumina content of 13%) having asize of 1 mm, which had been calcined at 500° C. for 4 hours in anelectric furnace, was dipped in a 1 N aqueous solution of sodiumhydroxide for 7 days and then washed with deionized water sufficiently.A glas column having an inner diameter of 30 mm was packed with 100 mlof the so prepared sodium type silica-alumina and 2,000 ml of an aqueoussolution containing 0.4 mole of silver nitrate was developed over aperiod of 7 days. The so treated silica-alumina was washed withdeionized water until no silver ion was detected in the washing liquidand it was then dried and calcined in the same manner as described inExample 12 to obtain a catalyst containing 0.6 milliequivalent of silverand 0.4 milliequivalent of Na per gram of silica-alumina.

By using the so prepared catalyst, a gas phase catalytic reaction wascarried out under the same conditions as described in Example 2 toobtain pyridine, 2-methylpyridine and 4-methylpyridine in yields of10.5%, 28.5% and 29.6%, respectively. The total yield of these threeproducts was 68.6% but the yield of high boiling point pyridine baseswas only 3.2%.

EXAMPLE 19

By using the same catalyst as prepared in Example 1, the reaction wascarried out for 10 hours under the same conditions as described inExample 2 to obtain results shown in Table 9.

                  TABLE 9                                                         ______________________________________                                        (SiO.sub.2 --Al.sub.2 O.sub.3 --WO.sub.3 Catalyst)                                   Yields (%) of Products                                                 Time (hours)                                                                           2-methylpyridine                                                                           4-methylpyridine                                                                           total                                      ______________________________________                                        0        33.4         45.7         79.1                                       3        33.5         45.8         79.3                                       6        31.0         44.4         75.4                                       10       30.2         43.4         73.6                                       ______________________________________                                    

EXAMPLE 20

By using the same catalyst as prepared in Example 12, the reaction wascarried out for 10 hours under the same conditions as described inExample 2 to obtain results shown in Table 10.

                  TABLE 10                                                        ______________________________________                                         ##STR19##                                                                             Yields (%) of Products                                               Time (hours)                                                                             2-methylpyridine                                                                           4-methylpyridine                                                                           total                                    ______________________________________                                        0          43.3         39.7         83.0                                     3          43.1         39.4         82.5                                     6          42.5         38.2         80.7                                     10         41.6         38.0         79.6                                     ______________________________________                                    

COMPARATIVE EXAMPLE 3

By using a silica-alumina catalyst (having an alumina content of 13%), agas phase catalytic reaction was carried out for 10 hours under the sameconditions as described in Example 2 to obtain results shown in Table11.

                  TABLE 11                                                        ______________________________________                                        (SA Catalyst)                                                                        Yields (%) of Products                                                 Time (hours)                                                                           2-methylpyridine                                                                           4-methylpyridine                                                                           total                                      ______________________________________                                        0        16.9         24.0         40.9                                       3        16.5         23.3         39.8                                       6        14.9         21.5         36.4                                       10       12.6         17.5         30.1                                       ______________________________________                                    

What is claimed is:
 1. A process for preparing pyridine bases comprisingreacting acetaldehyde with 0.5 to 3 times the molar amount of ammonia inthe gas phase at a temperature of 300° to 550° C. and at a spacevelocity of 200 to 10,000 hr⁻¹ in the presence of a catalyst prepared bycombining an oxidic or ionic salt containing a metal selected from thegroup consisting of tungsten, manganese, nickel, iron, molybdenum,uranium, lead and tin into silica-alumina simultaneously withpreparation of the silica-alumina.
 2. A process for preparing pyridinebases according to claim 1 wherein the silica/alumina weight ratio is inthe range of from 98/2 to 50/50.
 3. A process for preparing pyridinebases according to claim 1 wherein the catalyst contains the metalcompound in an amount of 1 to 70 parts by weight per 100 parts by weightof the sum of silica and alumina.
 4. A process for preparing pyridinebases according to claim 3 wherein said metal compound is a compound ofa metal selected from the group consisting of tungsten, manganese, leadand uranium and is present in an amount of 1 to 50 parts by weight per100 parts by weight of the sum of silica and alumina.
 5. A process forpreparing pyridine bases according to claim 3 wherein said metalcompound is a compound of a metal selected from the group consisting ofnickel, iron, molybdenum and tin and is present in an amount of 1 to 20parts by weight per 100 parts by weight of the sum of silica andalumina.
 6. A process for preparing pyridine bases according to claim 3wherein the catalyst comprises silica, alumina and a metal oxide, whichis prepared by admixing a mixture of silica in the form of silicahydrogel and/or silica sol and alumina in the form of alumina hydrogeland/or alumina sol with an aqueous solution of a compound of said metal,adjusting the pH of the resulting admixture to 6 to 8 to obtain a geland filtering, water-washing, drying and calcining the gel.
 7. A processfor preparing pyridine bases according to claim 3 wherein the catalystcomprises silica, alumina and a metal oxide, which is prepared by addingan aqueous solution of an aluminum salt and an aqueous solution of acompound of said metal simultaneously to silica hydrogel and/or silicasol, adjusting the pH of the resulting admixture to 6 to 8 to obtain agel and filtering, water-washing, drying and calcining the gel.
 8. Aprocess for preparing pyridine bases according to claim 3 wherein thecatalyst comprises silica, alumina and a metal oxide, which is preparedby admixing an aqueous solution of sodium silicate and an aqueoussolution of an aluminum salt with an aqueous solution of a compound ofsaid metal, adjusting the pH of the resulting admixture to 6 to 8 toobtain a gel and filtering, water-washing, drying and calcining the gel.9. A process for preparing pyridine bases according to claim 6 whereinsaid aqueous solution of the compound of the metal is an aqueoussolution of the metal salt of an acid selected from formic acid, aceticacid, propionic acid, lactic acid, oxalic acid, citric acid, nitricacid, sulfuric acid, hydrochloric acid, hydrobromic acid and metaloxyacid.
 10. A process for preparing pyridine bases according to claim 3wherein the catalyst comprises silica, alumina and a metal oxide, whichis prepared by admixing a mixture of silica in the form of silicahydrogel and/or silica sol and aluminum in the form of alumina hydrogeland/or alumina sol with a slurry of a hydroxide of said metal, adjustingthe pH of the resulting admixture to 6 to 8 to obtain a gel andfiltering, water-washing, drying and calcining the gel.
 11. A processfor preparing pyridine bases according to claim 3 wherein the catalystcomprises silica, alumina and a metal oxide, which is prepared byadmixing silica hydrogel and/or silica sol with an aqueous solution ofan aluminum salt and a slurry of a hydroxide of said metal, adjustingthe pH of the resulting admixture to 6 to 8 to obtain a gel andfiltering, water-washing, drying and calcining the gel.
 12. A processfor preparing pyridine bases according to claim 3 wherein the catalystcomprises silica, alumina and a metal oxide, which is prepared byadmixing an aqueous solution of sodium silicate and an aqueous solutionof an aluminum salt with a slurry of a hydroxide of said metal,adjusting the pH of the resulting admixture to 6 to 8 to obtain a geland filtering, water-washing, drying and calcining the gel.
 13. Aprocess for preparing pyridine bases according to claim 3 wherein thecatalyst comprises silica, alumina and a compound of the metal, which isprepared by admixing a mixture of silica in the form of silica hydrogeland/or silica sol and alumina in the form of alumina hydrogel and/oralumina sol with an aqueous solution of a water-soluble compound of saidmetal to obtain a gel and filtering, water-washing, drying and calciningthe gel.
 14. A process for preparing pyridine bases according to claim13 wherein said water-soluble compound of the metal is selected fromMnSO₄, NiSO₄, Fe₂ (SO₄)₃, UO₂ SO₄, MnCl₂, NiCl₂, UO₂ Cl₂ and NaWO₄. 15.A process for preparing pyridine bases according to claim 3 wherein thecatalyst comprises silica, alumina and a relatively water-insoluble saltof the metal, which is prepared by admixing a mixture of silica in theform of silica hydrogel and/or silica sol and alumina in the form ofalumina hydrogel and/or alumina sol with an aqueous solution of acompound of said metal, adding a precipitating agent to the resultingadmixture to precipitate said metal in the form of a relativelywater-insoluble salt to obtain a gel and filtering, water-washing,drying and calcining the gel.
 16. A process for preparing pyridine basesaccording to claim 15 wherein said compound of the metal is an aqueoussolution of the metal salt of an acid selected from formic acid, aceticacid, propionic acid, lactic acid, oxalic acid, citric acid, nitricacid, sulfuric acid, hydrochloric acid, hydrobromic acid and metaloxyacid.
 17. A process for preparing pyridine bases according to claim16 wherein said relatively water-insoluble salt is a chloride of themetal and said precipitating agent is selected from HCl, NaCl and KCl.18. A process for preparing pyridine bases according to claim 16 whereinsaid relatively water-insoluble salt is a fluoride of the metal and saidprecipitating agent is selected from NaF, NH₄ F and KF.
 19. A processfor preparing pyridine bases according to claim 16 wherein saidrelatively water-insoluble salt is a sulfate of the metal and saidprecipitating agent is selected from H₂ SO₄ and Na₂ SO₄.
 20. A processfor preparing pyridine bases according to claim 16 wherein saidrelatively water-insoluble salt is a phosphate of the metal and saidprecipitating agent is selected from H₃ PO₄, Na₃ PO₄, K₃ PO₄, (NH₄)₃PO₄, Na₂ HPO₄, K₂ HPO₄ and (NH₄)₂ HPO₄.
 21. A process for preparingpyridine bases according to claim 1 wherein acetaldehyde and ammonia areseparately preheated to a temperature of at least 200° C. and then, theyare mixed together and contacted with the catalyst.
 22. A process forpreparing pyridine bases according to claim 1 wherein a gas mixture ofthe acetaldehyde and ammonia is preheated to 300° to 550° C. before themixture is contacted with the catalyst.
 23. A process for preparingpyridine bases according to claim 1 wherein the gas phase catalyticreaction is carried out in the presence of a diluent selected from thegroup consisting of steam, helium, argon and nitrogen.
 24. A process forpreparing pyridine bases according to claim 1 wherein the reactiontemperature is in the range of from 350° to 500° C.
 25. A process forpreparing pyridine bases according to claim 1 wherein the space velocityis in the range of from 400 to 2,000 hr⁻¹.